This invention relates to the addressing of arrays of electrical elements and concerns a multiplexer circuit for reading the signals from elements of such an array or addressing those elements. In particular, the invention concerns a multiplexer circuit for reading or addressing an array of device elements formed with thin-film circuitry. The device elements may be image sensor elements (for example photosensitive diodes) of a large area image sensor, or display elements of a flat panel display (for example a liquid crystal display), or several other types of device element.
Addressing an array of device elements in rows and columns on a large area circuit requires each element to be connected to a unique pair of row and column conductors. In the case of an image sensor, a resolution of 300 dpi (dots per inch) may be required so that for an A4 large area image sensor, 2,500 and 3,500 rows and columns are required respectively (with the rows parallel to the long side of the A4 page). Problems therefore arise in forming the interconnections to the large area circuit and the use of multiplexer circuits which are integrated with the large area circuit is desired, so as to reduce the number of connections to the integrated circuit.
U.S. Pat. No. 5,148,030 discloses a photon counting type radiation image detecting apparatus having a reading circuit which enables the number of lead wires from the pixel sensing array to an image display device to be reduced. When a pixel detects the presence of a photon, an associated circuit generates a binary word which represents that pixel, and the circuit also outputs a signal indicating the level of energy of the incident photon. Thus, an output for each pixel is no longer required in order to determine which pixel is active. Instead, only as many outputs are required as there are digits in the binary word representing each pixel. However, the circuit of U.S. Pat. No. 5,148,030 does not enable addressing of each pixel of the array and also relies upon the fact that photons are only incident upon one pixel at any time.